1. Field of the Invention
In general, this invention relates to infusion catheters. More specifically, this invention relates to an intraparenchymal infusion catheter system for delivering a therapeutic agent into an organism where the catheter has a porous tip which has a perfusion surface area that may be matched to the target volume.
2. Description of the Related Art
When chronic administration of a pharmaceutically active agent is required, internal delivery by an external infusion pump or an implantable infusion pump (xe2x80x9cIIPxe2x80x9d), in combination with a catheter, may be the desired delivery means. For example, IIP-catheter delivery may be preferred when, for example, the site specific delivery of the drug is critical, or the drug must be administered in tightly controlled, yet minute dosages.
In current catheter designs, the delivered agent ordinarily flows out of the catheter via a fixed number of elution holes. Most catheter designs utilize either a single elution hole or a few elution holes. The current designs suffer from at least two notable disadvantages. To begin with, the fixed number of elution holes may make it difficult to tailor the catheter to the drug flow rates dictated for a particular drug and a particular parenchymal target. In many neurological applications, the quantity of delivered drug is relatively minute and must be carefully tailored. Some flexibility in flow rate is achieved by calibrating the IIP, although it is still desirable to be able to more carefully tailor the number of elution holes to the desired flow rate. In addition, current catheter designs present a fixed external perfusion surface area to a selected parenchymal target volume. Since the perfusion area is fixed, it may be difficult to match the perfusion area to the parenchymal target volume. For example, if the parenchymal target volume consists of a five centimeter long malignant mass, and the perfusion area of the catheter is only three centimeters in length, it may be very difficult to achieve infusion of a cytostatic agent through the entire length of the mass. Furthermore, there may be applications where it is desirable to minimize the volume displacement of the catheter tip into the selected parenchymal target in order to minimize tissue trauma. If the perfusion area of the catheter tip is fixed, no such tailoring is possible.
The present invention is directed at solving one or more of the above-noted problems.
A catheter system for delivering fluid to a selected site within an organism comprises a pump for delivering the fluid and a catheter coupled to the pump. The catheter comprises a first tubular portion that has a generally cylindrical lumen of a first internal diameter and is composed of a relatively impermeable material. A second tubular portion that has an open end is disposed within the lumen and a closed distal end is disposed without the lumen. The second tubular portion is composed of a flexible, porous material having a preselected microporosity that is operable to permit fluid to flow from the catheter into the organism. The second tubular portion is selectively moveable with respect to the first tubular portion.
Alternatively, a catheter for delivering fluid to a selected site within an organism comprises a first tubular portion that has a generally cylindrical lumen of a first internal diameter and is composed of a relatively impermeable material. A second tubular portion that has an open end is disposed within the lumen and a closed distal end is disposed without the lumen. The second tubular portion is composed of a flexible, porous material that has a preselected microporosity that is operable to permit fluid to flow from the catheter into the organism. The second tubular portion is selectively moveable with respect to the first tubular portion.